fix(pty): retain cleanup evidence through policy

.agents/notes/implemented/feature/2026-07-16-persistent-pty-sessions.md

@@ -34,7 +34,7 @@ Idle detection is backend behavior, not a second public seam. A remote or contai
 
 There are no plugin-load auto-start sessions. `terminal_open` creates a session only during an agent tool call, when ownership and the owning event-sourced session are known. A future declarative startup feature must compose through unpublished agent setup rather than create shared global terminals.
 
-Agent-scope disposal closes registrations first, then awaits quiescent teardown of every owned PTY. Unpublished backend setup is a tracked lifecycle operation: owner or service disposal aborts its service-owned signal, waits for backend settlement and rollback, and only then returns. Caller cancellation retains its exact `AbortSignal.reason` even when the backend rejects in response; a service rollback close failure rejects both the spawn and the disposing lifecycle, while `PtyBackendCleanupError` lets a backend preserve its own failed startup cleanup for the disposing lifecycle without replacing that caller reason. Backend or tool-plugin reload does not orphan sessions: ownership lives in `PtyService` until the agent ends, following the same service-owned-record pattern as [`ctx.tasks`](../../../../packages/tasks/tasks/README.md). The service reserves the session synchronously for one active send before returning its operation, including before a background task id becomes visible; a second send fails with `SEND_ACTIVE`, so output and cancellation cannot cross operation ownership.
+Agent-scope disposal closes registrations first, then awaits quiescent teardown of every owned PTY. Unpublished backend setup is a tracked lifecycle operation: owner or service disposal aborts its service-owned signal, waits for backend settlement and rollback, and only then returns. Caller cancellation retains its exact `AbortSignal.reason` even when the backend rejects in response; a service rollback close failure rejects both the spawn and the disposing lifecycle, while `PtyBackendCleanupError` lets a backend preserve its own failed startup cleanup for the disposing lifecycle without replacing that caller reason. When caller cancellation settles before disposal, the cleanup failure remains tracked owner activity until later owner or service disposal consumes and reports it, so sandbox-mode policy cannot mistake failed cleanup for quiescence. Backend or tool-plugin reload does not orphan sessions: ownership lives in `PtyService` until the agent ends, following the same service-owned-record pattern as [`ctx.tasks`](../../../../packages/tasks/tasks/README.md). The service reserves the session synchronously for one active send before returning its operation, including before a background task id becomes visible; a second send fails with `SEND_ACTIVE`, so output and cancellation cannot cross operation ownership.
 
 ### Security and process boundary
 
@@ -62,7 +62,7 @@ The ACP render contract is exact and location-free. `terminal_send` uses termina
 
 `terminal_send({ sessionId, text, submit?, run_in_background? })` treats `text` as UTF-8 bytes and resolves `submit` to `true` in the tool implementation. When `submit` is true it writes the platform Enter sequence after the text; when false it writes only the text, allowing control characters and REPL fragments without hidden content heuristics. `enableRunInBackground` defaults to true; false removes `run_in_background` from the schema and rejects the same undeclared argument if a caller forces it through execution.
 
-Foreground sends return a bounded rendered delta and two independent facts: `waitReason` (`stdin_read | inferred_idle | timeout | session_exit`) and `sessionStatus` (`running` or `exited` with exit code or signal). `session_exit` refers to the PTY's top-level shell process, not an arbitrary foreground command whose status the shell consumes. A timeout never implies process exit. `dsh-tool-pty.maxResultBytes` defaults to 262144, rejects values below 64 so creation acknowledgements retain registry-issued ids, and caps the complete UTF-8 result after normalized errors, wait, session, pagination, truncation, and generic task-status wrappers; the renderer reserves suffix space and preserves code-point boundaries instead of treating the backend payload cap as the final model bound.
+Foreground sends return a bounded rendered delta and two independent facts: `waitReason` (`stdin_read | inferred_idle | timeout | session_exit`) and `sessionStatus` (`running` or `exited` with exit code or signal). `session_exit` refers to the PTY's top-level shell process, not an arbitrary foreground command whose status the shell consumes. A timeout never implies process exit. `dsh-tool-pty.maxResultBytes` defaults to 262144, rejects values below 64 so creation acknowledgements retain registry-issued ids, and caps each single-text UTF-8 result after normalized errors, wait, session, pagination, truncation, generic task-status wrappers, pre-execute denials, and post-execute replacements or blocks; its outer post-execute wrapper leaves deliberately structured multi-block policy content unchanged. The renderer reserves suffix space and preserves code-point boundaries instead of treating the backend payload cap as the final model bound.
 
 With `run_in_background: true`, `dsh-tool-pty` registers the in-flight send on `ctx.tasks` and returns immediately with `taskId`. The producer places `maxResultBytes` on the task snapshot so `task_output`, terminal kill status, and completion notices enforce the same complete-result cap after generic metadata. `task_output(wait: true)` waits, reads incremental output, and records the final result; `task_kill` resolves the current foreground PGID and delivers a real `SIGINT`, including when the application has disabled terminal `ISIG`, and escalates only through the PTY backend's owned teardown path. If the task surface is absent, background mode fails before writing input. No PTY-specific `sleep` tool or general wake-up seam is added.